1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor template and more particularly, relates to a method of manufacturing a semiconductor template by attracting strains by means of microstructures.
2. Description
The development of green technology and green policy has been thriving these years, one of the objects which the industry seeks is a power amplifier with greater performance. An ideal power amplifier is small in size, light weighted, competitive in price, reliable, with high efficiency, able to provide high power density, and able to transmit within greater ranges and different temperatures. However, the use of silicon-based power electronic devices is almost reaching its limits in semiconductor industry. Therefore, it is important to introduce new materials for the future development of power devices.
At present, the operational frequency of Nitride HEMTs on a sapphire substrate has been applied to X-band (8-12 GHz). As Nitride HEMTs is gradually utilized and developed toward high-frequency band, the corresponding gate length is shortened, which results in the self-heating effect in Nitride HEMTs under the operations of high frequency, high bias voltage, high current, high power, and especially in high frequency band. Since the thermal conductivity of sapphire substrates is lower (0.4 Wcm−1K−1), the heat generated by the Nitride HEMTs is accumulated in the transistor, and thus the self-heating effect will limit the performance of transistors and cause damages.
The thermal conductivity of a sapphire substrate is 0.4 Wcm−1K−1 while the thermal conductivity of a SiC substrate is 4.9 Wcm−1K−1 and the thermal conductivity of a Si substrate is 1.5 Wcm−1K−1—both of them have higher thermal conductivity than the sapphire substrate and thus are favored by being the substrates of high-power and high-speed GaN-based devices. Although a high-power and high-speed GaN-based device including a SiC substrate has high performance in device characteristics, the costs on SiC substrates are too high. In consideration of costs on substrates, Si substrates are cheaper than SiC substrates and sapphire substrates.
It is described in an article of June, 2008, from Nitronex Corporation that when the large-sized substrates is used, the cost on every unit area of a Si substrate is one hundred times cheaper than that of an SiC substrate; thus, utilizing GaN high speed devices on Si substrates means money and business.
Meanwhile, LEDs have many advantages such as lower energy consumption, longer lifetime, faster reaction speed, etc.; therefore, LEDs have been gradually replacing traditional lights such as bulbs and fluorescent lamps. However, the luminous efficiency of LEDs has been a target that manufacturers go for. Thus, the luminous flux of LEDs is inspected all the time during the whole process of manufacturing so as to confirm whether the luminous efficiency of LEDs meets the expectation.
Generally speaking, blue LED chips are utilized as excitation sources by white LEDs in the market. Most blue LED chips include GaN or InGaN as primary materials for light emitting, and blue LED chips include GaN-based epitaxial layer depositing on sapphire substrates. (GaN-based epitaxial layer and sapphire substrate have the same crystal structure of hexagonal close-packed lattice form.) In order to improve the luminous efficiency of LEDs further, the sapphire substrate is patterned. Owing to the use of ordered arrangement of patterns in the sapphire substrate, internal quantum efficiency is improved, and light extraction efficiency is increased. As a result, the brightness of LEDs is enhanced.
However, although the brightness of LEDs including patterned sapphire substrates is increased, the lattice constant and the thermal conductivity of GaN-based epitaxial layer and of sapphire substrates are not matching. For example, the mismatch in the lattice constant of GaN-based epitaxial layers and that of sapphire substrate is up to 16%. Therefore, if GaN-based epitaxial layers are deposited on a sapphire substrate, defects such as point defects, dislocation defects and cracks are generated due to the partial relaxation of strains in GaN-based epitaxial layers.
When different substrates can be used to grow GaN-based epitaxial layers, users can either choose a SiC substrate or a Si substrate. In the consideration of costs, utilization of Si substrates in LEDs will be the mainstream in the future. However, the mismatches in lattice constant and in thermal conductivity between the GaN-based epitaxial layer and the Si substrate are greater than that between the GaN-based epitaxial layer and the sapphire substrate, which makes it even more difficult to grow GaN-based epitaxial layers on Si substrates without defects.
Thus, a method for manufacturing a semiconductor template balanced between strains and defects is provided according to embodiments of the present invention to avoid defects generated due to mismatches in lattice constant and in thermal conductivity between the GaN-based epitaxial layer and the substrate.